1. Field of the Invention
The present invention relates to an atomic layer deposition (ALD) apparatus, and particularly relates to an ALD apparatus that is suitable for rapidly depositing a thin film on a structure having a larger actual area than an apparent area, such as DRAM.
2. Description of the Related Art
In the manufacture of semiconductor devices, efforts for improving apparatuses and processes to be suitable for forming a high quality thin film on a substrate have continued. In ALD methods, separate pulses of at least two reactants are sequentially introduced on the substrate, a surface reaction of the reactants occurs to form a monolayer on the surface of the substrate, and the reactants are sequentially introduced until a desired thickness of the deposited material is deposited. In pure ALD methods, the reactants are pulsed separately, and temperatures are kept in a window above condensation and below thermal decomposition, the thin film is formed by saturative surface reactions, and thereby a thin film having a uniform thickness may be formed on the whole surface of the substrate regardless of surface roughness of the substrate and impurities in the thin film may be reduced to form a thin film having high quality.
A lateral flow ALD reaction chamber, in which gases flow laterally over and parallel to the major surface of a substrate, has been proposed. In the lateral flow ALD reaction chamber, flowing of the gases is rapid and simple and thereby high speed switching of gas supplies may be attained to reduce time required for sequentially supplying process gases. Exemplary lateral flow reaction chambers suitable for time-divided gas supply of an ALD method and a method of depositing a thin film using the lateral flow reaction chamber have been disclosed in Korean Patent Application Nos. 1999-0023078 and 2000-0033548, and U.S. Pat. No. 6,539,891. In addition, an improved example of the lateral flow reaction chamber suitable for time-divided gas supply of an ALD method and a method of depositing a thin film using the lateral flow reaction chamber have been disclosed in Korean Patent Application No. 2005-0038606 and U.S. patent application Ser. No. 11/429,533, published as U.S. Publication No. 2006-0249077 A1 on Nov. 9, 2006. Other examples of lateral flow ALD reaction chambers have been disclosed in U.S. Pat. No. 5,711,811 and U.S. Pat. No. 6,562,140. In the examples, the reaction chambers have a constant gap between the side on which a substrate is disposed and the side facing a surface of the substrate, such that gas flowing to the substrate may be constant and maintained in a state of a near laminar flow. such lateral flow reaction chambers are also referred to in the art as cross-flow or horizontal flow reaction chambers, although the orientation need not be horizontal.
A substrate with a rough surface having a plurality of protrusions and depressions has an actual surface area that is larger than a planar surface. In addition, in a dynamic random access memory (DRAM), a dielectric layer that stores charge and has a plurality of thin holes and drains may have an actual surface area of about fifty times as large as a planar substrate. Similarly, other integrated circuit patterns may have dense and/or high aspect ratio features that greatly increase surface area relative to planar surfaces.
In general, a substrate or wafer for a semiconductor integrated circuit may have a round planar shape.
If a substrate with a rough surface having an actual surface area of about fifty times as large as a planar substrate is set in a lateral flow ALD reaction chamber in which reactant gases supplied in a constant flux and a constant flow velocity, then the reactant gases supplied in a constant flux and a constant flow velocity on the substrate may be consumed in a different way relative to ALD on other substrates that do not have a rough surface. Accordingly, a gas supply of a constant flux and a constant flow velocity may not be optimal for the substrate with a rough surface having an actual surface area of about fifty times as large as a planar surface on a similar substrate, in that time required for a saturative gas supply cycle may be longer and the amount of gases required for the saturative gas supply cycle may be larger than optimally required.
In FIG. 1, a lateral flow ALD reaction chamber in which gases flow in the direction of the arrows, and a circular substrate set in the lateral flow reaction chamber, are shown schematically. Referring to FIG. 1, if the gases are supplied to the reaction chamber in a gas pulse flow in a constant flux and a constant flow velocity on the circular substrate with a rough surface having the actual surface area that is much larger than a planar substrate, portions of the gases are consumed in positions 300X, 300Y, and 300Z through adsorption or surface reaction on the surface of the substrate after portions of the gases are consumed through adsorption or surface reaction on the surface of the reaction chamber. Even though adsorption or surface reaction on the surface of the substrate in the positions 300X, 300Y, and 300Z is completed, adsorption or surface reaction on the surface of the substrate in a position 300W may not yet be completed, i.e., saturation may not be achieved. Accordingly, the gases must be supplied to the reaction chamber until adsorption or surface reaction on the surface of the substrate in a position 300W is completed. Thereby, the gases that flow on the positions 300X and 300Y after completion of adsorption or surface reaction in the positions 300X and 300Z and before completion of adsorption or surface reaction in the position 300W is excess and wasted. In other words, in order to achieve true surface saturation in all locations, full gas flow must be supplied to all locations until the last-to-saturate location is saturated.
If reactant gases have enough vapor pressure and an excess of reactant gases is supplied to the reaction chamber, these differences or different locations on the substrate may be ignored. For example, oxygen (O2) gas or ozone (O3) gas may be supplied at a much larger quantity compared with the minimum quantity required to form a thin film, such that differences in rates of saturation at different positions on the substrate may be ignored. However, it takes a great deal of time to supply a reactant gas having a lower vapor pressure such as tetrakis(ethylmethylamido)halfnium (TEMAHf) or tetrakis(ethylmethylamido)zirconium (TEMAZr), which are often employed to form a thin film of HfO2 or ZrO2. The same is true of numerous other precursors, including metal halides and metalorganics, that are suitable for ALD but have very low vapor pressures (e.g., less than about 0.1 mmHg) under standard (room temperature and atmospheric pressure) conditions.
For example, if a circular substrate having a diameter of about 300 mm and having the actual surface area about fifty times as large as a planar surface of 300 mm diameter is used, the time required for supplying the reactant gas until completion of adsorption or surface reaction on the whole surface of the substrate may be one second or more.
In addition, if the reactant gas supplied to the reaction chamber is not used to form a thin film but passes through the reaction chamber, a longer time is required for supplying the reactant gas until completion of saturative adsorption or surface reaction on the whole surface of the substrate.
Accordingly, in order to reduce the time required for supplying the reactant gas with a lower vapor pressure and/or in order to reduce the consumption of an expensive reactant gas, it is preferred that adsorption or surface reaction on the whole surface of the substrate is completed, or the surface saturated, with minimum supply of the low vapor pressure gas or the expensive gas.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.